a. Field of the Invention
The present invention pertains generally to an electrophysiological device and method for providing energy to biological tissue and, more particularly, to an ablation apparatus that includes a bipolar electrode that uses a flexible polymer electrode. The present invention is also directed to an electrophysiological device that can be used for drug delivery to a target tissue.
b. Background Art
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node located in the right atrium to the atrial ventricular (AV) node and then along a well defined route which includes the His-Purkinje system into the left and right ventricles. Sometimes abnormal rhythms occur in the atrium, a condition known as atrial arrhythmia. Three of the most common arrhythmia are: (1) ectopic atrial tachycardia, (2) atrial fibrillation, and (3) atrial flutter. Arrhythmia can result in significant patient discomfort and even death because of a number of associated problems, including: (1) an irregular heart rate, which causes a patient discomfort and anxiety; (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure; and (3) blood flow stasis, which increases the vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause for the arrhythmia, although it is believed that the principal mechanism is one or a multitude of stray circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included administering various drugs. In some circumstances, drug therapy is ineffective and frequently is plagued with side effects, such as dizziness, nausea, vision problems, and other difficulties.
For example, an increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia involves ablation of heart tissue to cut off the path for stray or improper electrical signals. Such procedures may be performed by catheters that incorporate ablation electrodes. Typically, the catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the catheter reaches the desired location for the ablation procedure in the heart. During the ablation procedure, the electrode of the ablation catheter is placed in contact with the target tissue and therapeutic substance is applied to the tissue via the electrode. Therapeutic substance may be a chemical substance; energy, such as thermal energy (heating or cooling); electrical energy, such as radiofrequency (RF) current; electromagnetic energy, such as light; and acoustic energy, such as ultrasound. Upon delivery of sufficient therapeutic substance to the tissue, the ablation procedure kills and/or irreversibly modifies the target tissue, and produces lesions. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate arrhythmia.
Efficacious delivery of therapeutic substance from the electrode to the target tissue requires that the electrode to be in optimal contact with the target tissue. Ensuring optimal contact between the electrode and the tissue is not readily achieved using rigid electrodes, such as metal electrodes. Several factors that may contribute to suboptimal contact include: (i) the remote manipulation of the catheter from the electrode, typically over four feet away; (ii) the constant movement of the heart wall; (iii) the variable compliance of the heart wall, and (iv) the highly contoured nature of the heart wall. Flexible polymer electrodes are designed to provide superior conformance with tissue than metal electrodes.